Shortcodes are THE single most important thing to know on the IP Office.
Wether it is as a System SC, User SC or in the ARS tables they all are made up of the same parts and understanding them will make your lives easier.
Code - this is what you dial from a phone and should not overlap with another Shortcode because if you have *24 as a SC you could not reach a code *24x any more except via voicemail transfer option of "en block" dialing. Placeholders can be used like x for a single digit or N for any number of digits but sometimes you have to add a ; (semi colon) at the end to tell the system that after the system timer expires (default 4 seconds) it starts dialing
Feature - this is the dropdown menu that will present you with all the options you have and some of those will actually limit the usability of the other fields (barred for example means you get the wave off tone[Turkey tone] and no matter what you put into the other fields it makes no difference)
Telephone Number - if this field is not eliminated by the Feature you chose then this is what the system will dial for you after you dialed the "Code". If you have a code with entries other than x and N then you have to also add it to this field. Code *24xxx for example needs *24N to dial the entire code dialed in case you want to send the whole dialstring of *24 plus the 3 digits via an SCN trunk or similar
Line Group ID - this is kind of self explanatory as it means that the "Telephone Number" field entry gets dialed on this Line Group ID which can be a Line or an ARS. !!! Keep in mind that not all Features are using this entry !!!
If you dial out via a code (9N - Dial - N - 50) like North American default then it means that anything past the 9 will be sent to the ARS where there are other Shortcodes that pick up and match the entries as either local or long distance calls and choose the lines accordingly. SIP trunks for LD and analog lines for local for cost savings if you are restricted on LD minutes etc.
Every setup is a little different but all SC's are adhering to the above rules and if they are cascaded with System SC's then ARS' then follow along and you will make sense out of them after screwing up once big time or hopefully sooner.
Good Luck and I hope this helps solving some mysteries about Shortcodes.